3of 10South Africa former President Nelson Mandela (right) meets with British scientist Professor Stephen Hawking in Johannesburg in 2008. Hawking has died at age 76, a family spokesman said Wednesday.Photo: DENIS FARRELL, AFP/Getty Images

4of 10Professor Stephen Hawking poses for photographs in his office at The Centre for Mathematical Sciences in Cambridge, in central England in 2007. Hawking has died at age 76, a family spokesman said Wednesday.Photo: LEON NEAL, AFP/Getty Images

5of 10FILE - MARCH 14: Renowned British Physicist Stephen Hawking has passed away at his home in Cambridge, March 14, 2018. NEW YORK, NEW YORK - APRIL 12: Professor Stephen Hawking onstage during the New Space Exploration Initiative "Breakthrough Starshot" Announcement at One World Observatory on April 12, 2016 in New York City. (Photo by Jemal Countess/Getty Images)Photo: Jemal Countess

6of 10U.S. President Barack Obama (right) presents the Medal of Freedom to physicist Stephen Hawking during a ceremony in the East Room of the White House in Washington, DC, in 2009. Obama presented the medal, the highest civilian honor in the United States, to 16 recipients during the ceremony. Hawking has died at age 76, a family spokesman said Wednesday.Photo: Chip Somodevilla

7of 10British cosmologist Stephen Hawking experiences zero gravity during a flight over the Atlantic Ocean in 2007. “It was amazing ... I could have gone on and on,” Hawking said after riding for two hours on a modified jet that flew a roller-coaster trajectory to create the impression of microgravity. Hawking has died at age 76, a family spokesman said Wednesday.Photo: ZERO G, AFP/Getty Images

8of 10Physicist Stephen Hawking appears in Berkeley in 2007. He addressed a sold-out crowd of 2,000 at Zellerbach Hall for the annual Oppenheimer Lecture in Physics. A second venue, Wheeler Hall, sold out 700 seats for a simulcast. Behind Hawking is a video screen displaying words from his lecture. Hawking has died at age 76, a family spokesman said Wednesday.Photo: Mark Costantini, SFC

9of 10British scientist Stephen Hawking attends the launch of The Leverhulme Centre for the Future of Intelligence (CFI) at the University of Cambridge, in Cambridge, eastern England. Hawking has died at age 76, a family spokesman said Wednesday.Photo: NIKLAS HALLE'N, AFP/Getty Images

10of 10Pope Francis (left) meets with English theoretical physicist and cosmologist Stephen Hawking at the Vatican in 2016. Hawking has died at age 76, a family spokesman said Wednesday.Photo: FILIPPO MONTEFORTE, AFP/Getty Images

LONDON — Stephen Hawking, whose brilliant mind ranged across time and space though his body was paralyzed by disease, has died, a family spokesman said early Wednesday.

“He was a great scientist and an extraordinary man whose work and legacy will live on for many years,” his children Lucy, Robert and Tim said in a statement.

The best-known theoretical physicist of his time, Hawking wrote so lucidly of the mysteries of space, time and black holes that his book, “A Brief History of Time,” became an international best seller, making him one of science’s biggest celebrities since Albert Einstein.

Even though his body was attacked by amyotrophic lateral sclerosis, or ALS, when Hawking was 21, he stunned doctors by living with the normally fatal illness for more than 50 years. A severe attack of pneumonia in 1985 left him breathing through a tube, forcing him to communicate through an electronic voice synthesizer that gave him his distinctive robotic monotone.

But he continued his scientific work, appeared on television and married for a second time.

As one of Isaac Newton’s successors as Lucasian Professor of Mathematics at Cambridge University, Hawking was involved in the search for the great goal of physics — a “unified theory.”

Such a theory would resolve the contradictions between Einstein’s General Theory of Relativity, which describes the laws of gravity that govern the motion of large objects like planets, and the Theory of Quantum Mechanics, which deals with the world of subatomic particles.

For Hawking, the search was almost a religious quest — he said finding a “theory of everything” would allow mankind to “know the mind of God.”

“A complete, consistent unified theory is only the first step: our goal is a complete understanding of the events around us, and of our own existence,” he wrote in “A Brief History of Time.”

In later years, though, he suggested a unified theory might not exist.

He followed up “A Brief History of Time” in 2001 with the more accessible sequel “The Universe in a Nutshell,” updating readers on concepts like super gravity, naked singularities and the possibility of an 11-dimensional universe.

Hawking said belief in a God who intervenes in the universe “to make sure the good guys win or get rewarded in the next life” was wishful thinking.

“But one can’t help asking the question: Why does the universe exist?” he said in 1991. “I don’t know an operational way to give the question or the answer, if there is one, a meaning. But it bothers me.”

The combination of his best-selling book and his almost total disability — for a while he could use a few fingers, later he could only tighten the muscles on his face — made him one of science’s most recognizable faces.

He made cameo television appearances in “The Simpsons” and “Star Trek” and counted among his fans U2 guitarist the Edge, who attended a January 2002 celebration of Hawking’s 60th birthday.

His early life was chronicled in the 2014 film “The Theory of Everything,” with Eddie Redmayne winning the best actor Academy Award for his portrayal of the scientist. The film focused still more attention on Hawking’s remarkable achievements.

Some colleagues credited that celebrity with generating new enthusiasm for science.

His achievements, and his longevity, also helped prove to many that even the most severe disabilities need not stop patients from living.

Hawking was born Jan. 8, 1942, in Oxford, and grew up in London and St. Albans, northwest of the capital. In 1959, he entered Oxford University and then went on to graduate work at Cambridge.

Signs of illness appeared in his first year of graduate school, and he was diagnosed with ALS, also known as Lou Gehrig’s disease after the New York Yankee star who died of it. The disease usually kills within three to five years.